On the two slabs, shirou pulled out the clay that he used to make the hagane for the sword, the clay of Iskandar`s crypt was mixed with charcoal from the forge that was powdered and Wheatstone powder that shirou had prepared. This mix looked black like tar and it gave the faint illusion of sucking in light.
On the second slab, he mixed the black clay from the crypt with red clay rich in iron oxide that the father and son had collected by themselves when shirou was out in a forest for survival training. The soil was retrieved from the location of a minor leyline so the mana conductivity was good enough.
This process that shirou was about to perform is the trademark quenching method of katanas, this is what gives them the curve they are known for. The clay that covers the blade is of different thicknesses at different places hence it gives rise to the curve, the beautiful patterns on the katana edge called "Hamon" and the blade is given the hard and sharp edge they are renowned for.
Shirou applied the black clay in a very thin layer on the edge of the blade using a scalpel. Then using a metal work pen he removed the clay from various places. originally shirou had planned to use chalk to mark the areas on the blade and then clay them but now with his increased support he was able to identify the optimal area by using magecraft.
He then applied a thick layer of red clay at the spine of the blade and then covered the middle remaining body of the blade with different clay according to his judgement. Putting down the tools he firmly placed his hand on the blade and both his hands glowed brightly with magic circuits as he tried to minutely scan the material. Rin understood how shirou every time felt when he used this spell, the information about molecular structure and alignment and a lot of useless information about the location of particles of impurities, beast bones, etc forced itself into her mind.
Still, she experienced it just for a moment as shirou was using her circuits to calculate and supplement his casting hence she just felt the strain on her circuits in the form of the heating up. Shirou scanned through the materials and mentally designed the best pathway for the flow of mana and here rin`s circuits came in the crutch, as she had cast 1000s of fin shots till now making it easy for him to trace the pathways the curse would take and he then used the metal working pen to scratch away the clay and draw circuits that then filled with the black clay of different thickness.
All this entwined at a grove on the tang, the tang had a few more similar groves that could fit things the size of the gem that shirou added inside the 1st grove. when the blade was covered in clay shirou took it to the forge and put a bar across the opening of the forge, using the bar as a support he dried the clay using the flames and when the clay became solid he pushed the blade into the opening. Then he poured charcoal above the blade and completely buried it inside the smouldering flames.
Using the tongues to use structural grasp on the blade he pumped the billow in a rhythm, the howling of the flames, the sound of pressurisation of air and the flickering firelight made the scene look like a festival if you ignore the strong scent of blood and ominous chill hidden under the glamour of the environment.
The boy repeatedly adjusted the position of the blade and rhythm of the flame. When he fully withdrew the blade it was shining red even when covered by clay, except the parts with the black covering stood out more like a stain in glass. He moved to a glass tank kept beside the forge and plunged the blade into it in a smooth motion.
The room witnessed the sudden eruption of a sizzling sound and water vapour erupted from the contact between red hot metal and water. The inside of the tank was not visible due to this as well but the water was not ordinary, it was collected from the river near where he collected the clay and after that, he constantly infused mana into it via his blood and saliva.
So this water contained weeks' worth of mana of the boy hence it began clearing when the blade started sucking the mana from the water like a whale. At this crucial moment, all the noises ceased to exist in his mind and he dived deeper into the blade, he kept diving deeper and deeper into it until suddenly as if a door had opened or a wall had been broken information began pouring into his head.
Shirou unconsciously released a grunt that Rin promptly mirrored. Due to her privileged pedigree and her own genius never had to strain her mana circuits, as all the things she did till now were achievable before her circuits were strained. But she experienced this for 1st time, the information shot like a shock through her circuits but she was unable to understand it clearly.
It was as if it was in an unknown language that she didn't know about so just understood by feeling, she understood things like concepts, demons, boon, blessings, favour, curses, and birth were present. Well her circuits were not specialised for this but the one standing beside it was born for this.
Shirou suffered through the information, he understood that what he was seeing now was the conceptual structure of the blade, he understood that somehow the process he did had become a form of worship and the sword had been received as a blessing.
He perceived with his mind as the blade slowly curved from the spine and he avoided it from warping by forcing mana into it. He witnessed the blade`s concept being solidified and the things he could understand increasing as he couldn't understand the properties of the materials now. The concept of a cursed demon blade solidified and in the outside world, the sword has already cooled down hence proving the quench was a success.
The demon blade was born in this distant era when all its compatriots were now ancient. This process of quenching is called yaki-re and is also the step where the soul is infused into the katana. The clay is a very good insulator hence the colling speed of the metal depends on how tic the layer of clay on it is, so the tickly covered spine colls slower and the thinly covered edge rapidly cools and lengthens and hardens achieving a complete crystal structure of steel whereas the softer still hot part of the spine folds backwards slightly to accommodate the hardening edge giving the blade it curve and hamon.
Kiritsugu lightly smiled at this success and Shirou's unfocused eyes focused, he understood that whatever this was it wasn't over. He knew what he had to do and looked at Rin, who looked into his eyes as if asking something, seeing him nod his head she passed him a cloth and a small piece of whetstone. Pulling the sword out of the now-muddy water they all witnessed that most of the mud had fallen off and the green topaz added on the tang released a reddish glow.
Rubbing the body of the blade with the whetstone, he wiped it off with the piece of cloth and rammed the prevalent mud. Then he moved back to the polishing stool and ground the sword on the whetstone giving it the silver colour of steel after he scraped off the upper parts. A beautiful wave like Hammon was present on the blade and the greyish blade had some form of charm that seemed to beckon people to hold it.
Looking at the sword shirou was filled with a sense of liberation and Rin removed her hand and sat down to relieve fatigue. It was already afternoon and the 3 of them had spent nearly 12 hours in this forge. Still before closing her sore circuits she perceived the environment and was puzzled to find that the ritual field had mostly disappeared but it had not completely ended as if something was remaining.
Shirou looked at the girl whose puzzled look covered in shoot and dust made her look adorable compared to her normal elegant and straight-laced facade. Shirou just smiled at Rin who was puzzled by the characteristic gentle smile of shirou that somehow made her feel something off.
Looking at the blade shirou caressed it as if it were a puppy and said
"You still lack a name. So you shall be named Phosphoric Fang."
The name left Rin stunned, she didn't notice the complete disappearance of the ritual field nor did she understand Shiro's sigh of relief at the blade being conceptually completed. She put her head down and blushed so much that her whole face was red. She was muttering things like
"What the hell is this guy thinking?"
(A/N: and end!!! This forging was a pain to write, but I still loved how it turned out.
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THANKS FOR READING:)